I have a program on one computer that is sending multicast packets. I can see the packets in Wireshark on that same computer, and on a different computer while in Linux, but not while in Windows (it's dual-boot).

The sending computer is wired into a router. The receiving computer is wireless. I'm using the same wireless NIC in both Linux and Windows. Any help would be greatly appreciated!

Just for future people searching: there was actually no problem with the packets being transferred, I simply had to use Microsoft Network Monitor to see them.

The link posted by multipleinterfaces goes into more detail, but long story short, on a Windows Vista or Windows 7 machine, Wireshark cannot capture packets in monitor mode, which was apparently what I needed to do.